This invention relates to dampers for torque converters and especially relates to such torque converters where coils springs are inserted in the torque transfer path between the turbine of the torque converter and an output shaft to a transmission to dampen sudden energy or torque changes between the turbine and the output shaft.
The utilization of “variable displacement” engines operating in four or eight cylinder mode has made engine vibration isolation more difficult and there is thus a need for a damper having increased control and damper capacity (torque absorbing capacity for storage as potential energy that can be released to smooth torque transfer) due to a torque increase in the engine. A lower rate, i.e., torque capacity per degree of wind up, is also desirable to improve noise vibration harshness (NVH), i.e., noise and vibration perceived by a driver or passenger in a vehicle. Current turbine dampers will not meet the torque capacity or NVH requirements needed for transfer of torque in four or eight cylinder modes of newer variable displacement engines to a transmission and vice-versa.
Single stage and even dual stage turbine dampers are already commercially available to reduce torque converter vibration isolation from the drive of an engine but still have serious problems with needed capacity and rate. Further such known turbine dampers may require a large envelope space, i.e., space taken by the damper in the power train and may have a large hysteresis, i.e., energy loss primarily through friction during damper operation.
It has been known that a series of complete dampers could accomplish the task of capacity and lower rate but not without serious disadvantages, in particular with respect to complexity in cooperative operation, expense, envelope space, hysteresis and balance.
An example of a known turbine damper may for example be found in U.S. Patent Publication US2004/0185940 . This damper operates by first compressing sets of springs 58A and 58B in series at an initial low rigidity, followed by springs 59 in parallel with 58A and 58B for an intermediate rigidity, followed by springs 60 in parallel with 58A, 58B and 59 for highest rigidity before lock up. This damper has a significant disadvantage, apparently not recognized by the inventors, in that the series of springs 58A and 58B are weak relative to 59 and 60. By the time springs 59 and 60 are able to enter in parallel, springs 58A and 58B will bottom out or nearly bottom out unless the weak springs only permit a small amount of initial wind up. Bottoming out causes outwardly bowing damaging forces on the springs. In understanding this it should be recognized that all springs are concentrically aligned.
A similar device is shown in U.S. Patent Publication US2004/0216979 except that the first sets of springs 11 in the form of dual spring sets where an internal spring is disposed within an outer spring so that only the outer spring initially operates, and the internal spring operates in parallel with the outer spring upon sufficient outer spring compression. Such an arrangement has definite disadvantages in that the inside spring must necessarily be of a smaller diameter than the outside spring and is thus usually significantly weaker. Such unmatched weakness can be partially offset by using thicker wire in the inside spring than used in the outside spring. This of course limits the usable strength of the outside spring by parameters unrelated to space and length. Further, the weaker spring can never be removed from torque transfer. Additionally, when it is desirable to match characteristics of the inside and outside springs, e.g., so the converter has similar characteristics in both rotational directions, such matching is difficult and in fact cannot be realistically completely accomplished due to the drastically different spring diameters. Another disadvantage is that multiple inventories of different spring types have to be maintained and properly used.
A second set of springs 15 is provided that operates in parallel with sets 11 when torque is sufficiently high.
U.S. Pat. No. 4,138,003 describes a damper having multiple series of springs, again where most springs are in nested sets with all of the disadvantages described above.